This invention relates to processing of mail items and in particular to systems for charging postage costs to a user of a postal service and for enabling verification that postage has been has been paid in respect of each postal item handled by the postal service.
As an alternative to the affixing of postage stamps purchased from a Postal Authority, franking machines are used to print a franking impression representing a selected postage charge on mail items. Such machines include a printing device for printing the franking impression and accounting means to maintain a record of accumulated value of postage used in franking and, when prepayment for postage is required, a record of credit remaining available for use in franking. The records maintained in the franking machine form the basis on which accounting and payment for postage charges incurred by a user is effected to the Postal Authority. Accordingly it is necessary that the records maintained in the franking machine are accurate and that the records cannot be tampered with in an attempt to defraud the Postal Authority. In order to ensure integrity of the data of the records when stored in electronic memory devices in the franking machine it is common to provide four sets of registers to store identical copies of the data. In operation of the franking meter, the data stored in the different sets of registers is checked periodically, for example prior to each franking cycle, to ascertain if the data in the register sets is identical. If any disparity is found between the records, the meter is caused to lock and prevent further franking until it has been checked by an authorised service engineer. By providing four sets of records, the data can be recovered from three of the sets of registers if one set is found to be storing erroneous data. In order to prevent attempts to use the meter fraudulently, unauthorised access to the registers and accounting circuits of the franking meter is physically inhibited by housing sensitive portions of the meter in a secure housing sealed by the Postal Authority. The need for provision of multiple sets of non-volatile registers to ensure integrity of the stored data and the need for physical security results in the manufacturing costs of franking meters being high.
Periodically, the franking meter has needed to be taken to the Postal Authority so that the Authority can check usage of the meter and obtain payment for the value of postage used. Where prepayment is required, the meter is taken to the Postal Authority whenever the amount of credit remaining recorded in the meter has decreased to a low value to enable the Postal Authority to reset the meter with additional credit in return for a further prepayment. In order to overcome the disadvantages inherent in the need for periodic return of the meter to the Postal Authority, reading of the contents of the registers and resetting the credit register may be carried out by communication via telephone connection with a resetting computer located at a Postal Authority centre. Alternatively register contents can be transferred from the meter to the resetting computer and credit resetting data transferred from the computer to the meter by means of a module containing an electronic data store and which can be connected alternately to the franking meter and the resetting computer and transported therebetween by the postal service.